The use of wheels is desirable in connection with different floor care appliances, such as vacuum cleaners and nozzle heads for vacuum cleaners.
To reduce costs, such wheels are normally very simple. Wheels are often formed as a unitary rigid plastic part and sometimes are provided with a tread surface of elastic plastic or rubber. One disadvantage with such a simple wheel structure is that the wheels are quite noisy during use since they can not provide proper sound damping when moved over a floor having a hard surface or when hitting an obstacle such as a doorstep or the like. Such floor care appliances are normally adapted to be used indoors and the noise generated can be very disturbing, especially during late hours or in environments where it is desirable to maintain silence.
Normally, wheels having inflatable tires are not an option for this kind of appliances because such types of wheels often are too expensive to manufacture, need maintenance in the form of occasional pumping, and are susceptible to puncture. Moreover, these kinds of appliances are normally too lightweight for inflatable wheels to be able to provide proper resilient properties and hence damping. Also, inflatable wheels are restricted in terms of alternative design options.
One possibility to overcome the disadvantages above, would be to manufacture the wheel of a soft and elastic plastic, such as foam plastic, which could provide the desirable damping properties. However, such soft plastics are often not sufficiently durable and wear resistant. Also the grip of the wheel with the floor will often be too good, which sometimes is undesirable when the appliance needs to be moved laterally without rotating the wheels. A wheel of this type is disclosed in DE 19712138, wherein a wheel body of a soft and elastic material is sandwiched between two stiffening disks. A similar wheel is disclosed in EP 716938.
In U.S. Pat. No. 5,255,410 is disclosed a wheel, which has a wheel body of a hard material and in a preferred embodiment is assembled of two matching partial wheel elements. The wheel body comprises a circumferential groove in which is positioned an elastic, annular tire having a portion protruding beyond the circumference of the wheel body. Underneath the bottom surface of the tire, there is preferably a deflection space to allow deflection of the tire. The object of this structure is to make it possible to use a tire material having high wear resistance and still achieve a high damping effect. However, this structure allows only for a limited deflection of the tire and hence a low damping effect. Also, a large part of the circumference of the hard material wheel body is exposed on each side of the tire which can bump into obstacles during use and cause unwanted noise.
Another type of a wheel having a damping effect is disclosed in EP 858760. Here, the wheel is formed with an inner support ring and an outer roller ring, which roller ring is manufactured of an elastic material and along one lateral edge is attached to the support ring whereas the opposed edge is free and disposed at a distance from the support ring. Accordingly, the support ring provides for the load-carrying structure whereas the roller ring provides for the damping feature since it can deflect elastically. However, there are several disadvantages associated with such a wheel. Although the roller ring is elastic it is also made of a hard material which, when rolling over a floor, can cause disturbing noise, especially if the floor is covered by sand or other kinds of debris. Moreover, the construction of the wheel has the effect that the diameter of the wheel, and hence the ground clearance, will vary to a large extent depending on the load applied on the appliance. The contact surface of the roller ring against the floor will also be inclined for most of the load situations, which can cause the wheel to deviate in one direction when rolling over the floor. The design of the wheel having one support ring and one roller ring located concentric with a small gap there between, may also cause debris to stick inside the gap which, as the debris build up, eventually will restrict the deflecting action of the roller ring.